HAND-BOOK OF PHYSIOLOGY. 



6'. As a packing material, fat serves very admirably to fill up spaces, 

 to form a soft and yielding yet elastic material wherewith to wrap tender 

 and delicate structures, or form a bed with like qualities on which such 

 structures may lie, not endangered by pressure. 



As good examples of situations in which fat serves such purposes may 

 be mentioned the palms of the hands and soles of the feet, and the orbits. 



FIG. 38. Branched connective-tissue corpuscles, developing into fat-cells. (Klein. ) 



d. In the long bones, fatty tissue, in the form known as yellow mar- 

 row, fills the medullary canal, and supports the small blood-vessels which 

 are distributed from it to the inner part of the substance of the bone. 



II. CAKTILAGE. 



Cartilage or gristle exists in three different forms in the human body,, 

 yiz., 1, Hyaline cartilage, 2, Yellow elastic cartilage, and 3, White fibro- 

 cartilage. 



Structure of Cartilage. All kinds of cartilage are composed of 

 cells imbedded in a substance called the matrix : and the apparent differ- 

 ences of structure met with in the various kinds of cartilage are more due 

 to differences in the character of the matrix than of the cells. Among 

 the latter, however, there is also considerable diversity of form and size. 



With the exception of the articular variety, cartilage is invested by a 

 thin but tough firm fibrous membrane called the pericliondrium. On the 

 surface of the articular cartilage of the foetus, the pericliondrium is rep- 

 resented by a film of epithelium; but this is gradually worn away up to- 

 the margin of the articular surfaces, when by use the parts begin to suffer 

 friction. 



Nerves are probably not supplied to any variety of cartilage. 



1. Hyaline Cartilage. 



Distribution. This variety of cartilage is met with largely in the 

 human body investing the articular ends of bones, and forming the 

 costal cartilages, the nasal cartilages, and those of the larynx with the ex- 



